1. Field of the Invention
The present invention relates to an antenna device including a coil element, and to an electronic appliance including the antenna device.
2. Description of the Related Art
For example, Japanese Unexamined Patent Application Publication No. 2014-75775 discloses an antenna device in which a planar conductor of an electronic appliance is used as a portion of a radiating element. The antenna device is configured such that a coil antenna, which is connected to a feeder circuit, couples with a loop formed by the planar conductor, and the planar conductor acts as an antenna radiating body.
A large portion of a casing of an electronic appliance, such as a mobile terminal device or an information processing device, is frequently formed of a metal member in order to increase the mechanical strength of the casing and to improve freedom of design. Consequently, a coil antenna mounted on a circuit board is often covered by a metal portion of the casing.
In an antenna device in which a planar conductor, such as a ground conductor pattern, formed on a circuit board of an electronic appliance is used as a radiating body, when a coil antenna mounted on a circuit board is covered by a metal portion of the casing, magnetic flux that passes through the coil antenna does not flow in a large loop to outside the casing and the communication characteristics are severely degraded. This phenomenon was discovered by the inventors of the present invention described and claimed in this application.